In recent years, metal cutting saw blades have undergone a variety of changes and modifications in numerous attempts to solve an array of problems associated with the cutting of difficult-to-cut materials that are prone to work hardening. In the past saw blades of various types have been produced with teeth of equal height and with teeth laterally set outward on opposite sides of the sawing plane of the blade, thereby serving to widen the kerf being generated by the blade so that clearance will be provided between the body of the blade and the side walls of the kerf.
Although such laterally set teeth have been found to function in a satisfactory manner for their intended purposes, when cutting materials that are prone to work hardening, the cutting efficiency may vary significantly depending on the relative heights and the amount of set on the set teeth and how the teeth are located in relation to other teeth on the blade. For example, when cutting such difficult-to-cut materials, blades having both set and unset teeth of uniform height and in which the teeth set extend outwardly the same distance from the centerline of the blade, the results are frequently uneven tooth penetration into the work thereby causing uneven wear, work hardening and deviation from straight cutting. In addition, when the set teeth extend to different distances outwardly from the centerline of the blade, other problems result which have given rise to various problematic tooth arrangements.
The focus of such problematic arrangements has been the relative location in each group of teeth of the set teeth with respect to the unset teeth. In attempting to solve such problems, for example, it has been found that an important factor in blade performance is controlling the lateral forces acting on the blade as a result of the sequence or relative location in each group of teeth of the widest or most heavily set teeth in relation to the unset and slightly set teeth. Indeed, although those skilled in the art of band saw blades have recognized the adverse effects on the operation of such blades caused by excessive blade vibration or "noise", they have failed to propose any particular saw tooth arrangement which has provided a completely satisfactory solution for such problems. One proposed solution has been to avoid the use of equally spaced teeth which have a tendency to produce resonant frequencies and cause excessive blade wear and metal fatigue which reduces the useful life of the blade.
Further, efforts to solve such problems have resulted in many different saw blade tooth arrangements that include repeating patterns of teeth on a blade. Typically, each pattern or group includes at least one high, unset, leading tooth followed by a plurality of trailing teeth of gradually decreasing height and increasing set. For example, U.S. Pat. No. 4,557,172 to Yoneda shows a variety of embodiments form of redundant groups of teeth are arranged sequentially along the saw blade. Additionally, many of such tooth arrangements have utilized varying pitch distances between the cutting tips of adjacent teeth to decrease the detrimental effects vibrations occurring at the resonant frequency of the tooth pattern.
Such tooth patterns have often resulted in unforeseen problems, especially in the case of cutting materials, prone to work hardening, such as stainless steel. Where a pattern utilizes teeth of varying heights but with only one level of set as disclosed in '172 Patent to Yoneda some of the teeth bear the load of maximum penetration and while others have a shallow depth of penetration and load or, as mentioned in Yoneda, do not cut at all. In cutting a material prone to work hardening using a blade of the type disclosed in the Yoneda Patent, the lower set teeth have the tendency of fretting or rubbing the surface of the workpiece thereby resulting in work hardening of the already hard material and making it even harder to cut. Further, as seen in U.S. Pat. No. 4,813,324 to Yoshida, et al, some recent saw blade designs utilize unset leading teeth and set trailing teeth, wherein the amount of set is related to the relative heights of the trailing teeth. Tests, however, have shown that blades which embody the claimed invention in Yoshida, et al, suffer significant levels of blade deviation when used on difficult-to-cut materials, especially when cutting at increased feed rates. Such deviations are apparently caused by those trailing teeth that have the greatest amount of set, having cutting edges that are displaced farthest from the blade's centerline or sawing plane and have substantially greater lateral displacement than the lighter set teeth. Upon contact with the material being cut, the wider set teeth transfer a greater lateral force to the blade than do the trailing teeth that are set closer to the sawing plane. It is postulated that such lateral forces imparted to the blade by the heavier set teeth must be compensated for, or countervailed, as quickly, or as closely, as possible to the point at which the application of that lateral force occurs in order to reduce or minimize the effects of such wobble or lateral deviation of the blade with the resulting detrimental effects of such vibrations.
Generally, and as disclosed in U.S. Pat. No. 4,557,172, for example, it has been suggested in the prior art that improved blade wear can be attained by using teeth of varying height and pitch distances between adjacent teeth which help to solve the problem of excessive vibration or "noise", particularly troublesome when cutting difficult-to-cut materials. In many of the prior patents, groups of teeth comprised of teeth of varying height and set are generally arranged along the blade in redundant or repetitive patterns. U.S. Pat. Nos. 4,727,788; 4,813,324; 4,827,822; and 4,958,546 are exemplary of such prior art saw blades in which various groups of teeth of different heights and sets are arranged in repetitive patterns. In each group of teeth a specific number of set teeth are arranged in the cutting order of: a high, unset, leading tooth followed by various arrangements of set teeth of different heights and lateral sets. For example, significant problems have been found even for those blades which are disclosed and claimed in the above referenced U.S. Pat. No. 4,813,324 to Yoshida, et al, as the nineteenth embodiment, and which blades have been manufactured and sold commercially by Amada Company of Japan. In disclosing that embodiment, the '324 Patent describes a perceived advantage in a nonconsecutive arrangement in each group of teeth of the two shortest and widest trailing teeth, as depicted in FIGS. 14(a)-14(c). It is suggested in that patent, that the arrangement as described and claimed therein has an advantage over the prior art in that the higher teeth, i.e., the unset and lightly set teeth, which bear most of cutting load, are only subjected to work loads corresponding to one pitch distance since there is no more than one lower tooth immediately preceding any of the higher load bearing teeth. According to the '324 Patent, tooth patterns having two consecutive shorter teeth would be unacceptable because there would necessarily be two pitch distances preceding at least some of the higher load-bearing teeth, resulting in greater wear of such teeth. Tests have shown, however, that the claimed invention of the '324 Patent suffer significant levels of lateral deviation or "wobble" and require substantially higher levels of cutting force than in blades that are not subjected to such levels of deviation. Apparently, the lateral vibrations produced by the arrangement of two nonconsecutive teeth of wider set results in uneven work loads on the unset and slightly set teeth, which normally assist in stabilizing or guiding the tracking of the blade. The resulting lateral deviation causes uneven wear of the cutting edges of the "guiding" teeth and can eventually lead to premature blade failure.
It has been found that various types and, in particular, band saw blades currently available in the marketplace generally fail to make square cuts over their useful life particularly when cutting materials prone to work hardening and it is postulated that this deficiency is caused by the arrangement of the guiding teeth in relation to the heavy set teeth.
Accordingly, it is the general object of the present invention to provide an improved saw blade construction that overcomes the drawback of the prior art.
It is another object to provide a saw blade that includes cutting teeth disposed to achieve more uniform loads during cutting so that the teeth will wear more uniformly than in blades hereto available.
It is a further object to provide a saw blade with its teeth arranged to cut to uniform depths of penetration, to reduce wear of the teeth and produce more uniform chip size.
It is yet another object to provide a saw blade construction that provides reduced vibration and noise during cutting.
It is also an object to provide a saw blade that reduces problems of work hardening of the material being cut.
It is yet another object to provide a saw blade construction characterized by reduced deviation and out-of-square cutting of the work.
The above and other objects and advantages of this invention will become more readily apparent when the following description is read in conjunction with the accompanying drawings.